The present invention relates to the field of lighting. It finds particular application to surgical lights and will be described with particular reference thereto. It is to be appreciated, however, that the present invention may also find application in conjunction with other types of non-surgical lighting systems.
Surgical lights used to illuminate surgical sites generally include one or more lamps disposed inside the dome of a dome-shaped reflector which directs light from the lamp to the area to be illuminated. Surgical lights are generally suspended above an operating table by one or more adjustable, articulated arms so that the lamp can be positioned as necessary during surgery.
Typically, surgical lights employ a lamp such as a tungsten halogen lamp which is positioned at or near the focal point of the dome-shaped reflector. The light from the lamp is reflected downward by the reflector through an optical lens or refractor positioned at a lower surface of the light fixture. The refractor is particularly designed to coordinate with the reflector to direct the light in a defined column or cone to an illumination zone. A typical refractor for a surgical lighthead includes up to many thousands of prisms each having a specific prescription in order to direct the light from the reflector to the illumination zone.
In order to prevent shadows when the surgeon's hand or head passes between the lamp and the patient, the reflector is generally quite large and focuses the light at an illumination zone which is the same size or smaller than the refractor. The refractor functions as a diffuser to diffuse the light which helps to prevent shadows. The diffuse light also helps to prevent the image of the filament from appearing prominently in the illumination zone. The size of the illumination zone in most surgical lights can be adjusted by a rotatable sterile handle provided at the center of the face of the light head.
A typical tungsten halogen lamp used in surgical lights includes a tungsten filament that emits energy when electric current passes through the filament. These lamps emit visible light and also emit ultraviolet, infrared, and other undesirable energy. In fact, about 81 percent of the input power to a lamp of this type is converted to infrared energy. However, if this infrared energy is directed to a surgical site, heating of the surgical site will occur which may cause tissue damage. Removal or filtering of the infrared energy from the light directed to the surgical cite to prevent tissue damage may be accomplished by one or more different devices including heat absorbing glasses, cold mirror coatings, and hot mirror coatings. Hot and cold mirror coatings are called dichroic coatings and transmit energy of some wavelengths while reflecting energy of other wavelengths.
The reflectors and refractors which are used in many known types of surgical lights are large precision devices formed of glass which is coated with a dichroic coating material. One of the drawbacks of the known surgical lightheads is that the reflectors and refractors, due to the use of glass and their large size, are extremely heavy and are expensive to manufacture. The refractor is particularly expensive because of the thousands of individual prescription prisms, generally constituting about 12% of the cost of the lighthead.
It is important that the light field or illumination zone created by a surgical light, when focused on a planar surface, have a consistent uniform intensity at all diameters of the zone when viewed by the human eye. However, if the light zone has a completely uniform intensity, the human eye will perceive the edges of the light zone as having a higher intensity than the center. Thus, the light intensity should be manipulated to have a desired intensity profile which will appear constant and uniform to the human eye.
In addition, the human eye is most sensitive to light in approximately the center or the green portion of the visible light spectrum. Thus, a light which has more green and less of the other visible light colors is most desirable for surgical lighting applications. However, one of the drawbacks of known surgical lights is that typical lamps, such as tungsten halogen lamps, used in these surgical lightheads do not have a desirable visible light color distribution.
The present invention contemplates a new and improved surgical lighthead and technique for overcoming the above-referenced drawbacks and others.